This application claims the priority of German Application No. 197 16 916.3, filed Apr. 23, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an internal combustion engine and, more particularly, to an internal combustion engine having an adjustment device for an exhaust camshaft, an ignition device, and a control device for controlling the adjustment device and the ignition device, as well as a method for operating an internal combustion engine.
An important development goal in modern internal combustion engines is to reduce pollutant emissions. Previous development activities had focused particularly on optimization of the exhaust scrubbing system. Modern exhaust scrubbing systems have since achieved pollutant conversion rates of over 97% so that further reduction of pollutant emissions by exhaust treatment systems is no longer possible.
Hence the goal of the invention is to provide an internal combustion engine as well as a method for operation of an internal combustion engine by which pollutant emissions can be further reduced and stricter limits for pollutant emissions can also be met, like those required for example for ultra low emission vehicles, or ULEV.
This goal is achieved according to the invention by an internal combustion engine and, more particularly, by an internal combustion engine having an adjustment device for an exhaust camshaft, an ignition device, and a control device for controlling the adjustment device and the ignition device. The control device retards the exhaust camshaft in a partial load range of the engine and retards an ignition timing point of the ignition device. The invention is based on the discovery that a definite decrease in raw emissions from an internal combustion engine is necessary for further reduction of pollutant emissions and for meeting stricter limits.
According to the invention, it is proposed to control a device provided for adjusting the exhaust camshaft in a partial load range in such fashion that the exhaust camshaft is retarded. At the same time, an ignition control device ensures that the ignition timing is retarded. Shifting the ignition timing results in a further decrease in HC emissions. At the same time, the reduced specific fuel consumption achieved by shifting the exhaust camshaft is compensated once again. On the whole, however, the specific HC emissions of the internal combustion engine are decreased significantly by combining these two measures.
Advantageous improvements on the invention are described herein.
An especially advantageous design for the two measures described above can be achieved by the ignition timing being retarded to the point where the improvement in specific fuel consumption achieved by adjustment of the exhaust camshaft is again essentially compensated. In this design, a significant reduction in HC emissions is achieved without specific fuel consumption being increased. At the same time, retardation of the ignition timing increases the exhaust temperature, resulting in faster heating of an exhaust system connected downstream from the engine.
Raw emissions can be further reduced by using an adjusting device for the intake camshaft. By advancing the intake camshaft in addition to adjusting the exhaust camshaft as described above, both the specific HC emissions and the specific fuel consumption can be further reduced. Once again, for optimum reduction of HC emissions, the ignition timing can be adjusted so that maximum reduction of HC emissions is achieved while keeping specific fuel consumption constant.
A change in the stroke of the intake camshaft, which is also provided, provides an additional opportunity for reducing raw emissions from the engine, since when the valve stroke is shorter, the intake means can be advanced even further for geometric reasons.
The two additional measures for influencing the intake camshaft have the goal of bringing the overlap range between the exhaust and intake valves into an optimum position (that is, the range in which the intake and exhaust valves are opened simultaneously) as well as the point in time when the intake valves close. This optimum position depends upon the combustion conditions within the engine and therefore must be determined individually for every engine. In particular, if the optimum value of the overlap range is exceeded, the combustion process deteriorates rapidly and thus produces a sudden rise in raw emissions. As a result, limits are imposed on the influence exerted on the intake camshaft.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.